In conventional servo valve design the servo valve used in a fluid flow system, has provided in association therewith:
a spool valve; and PA0 a restrictor arrangement in a hydraulic fluid system which effects movement and control of the spool in the spool valve. PA0 at least one electrical winding; PA0 an armature; PA0 a flapper means securely fixed to the armature; and PA0 a feedback arrangement attached to the flapper means; PA0 a servo valve made in accordance with the present invention; PA0 a spool valve, the position of the spool in which is controlled by the servo valve; and PA0 a feedback arrangement including a flow feedback member, the movement of which is dependent on the fluid flow through the system.
In operation an input current is applied to a torque motor in order to generate a torque which displaces an armature and thereby a flapper means attached thereto. The displacement of the flapper means creates a pressure imbalance in the hydraulic fluid system controlling the position of the spool within the spool valve, in response to which the spool in the spool valve is moved.
The movement of the spool in the spool valve causes the adjustment of a force resulting from the fluid flow through the system exerted upon the servo valve in a feedback arrangement which is linked to the armature. Eventually, an equilibrium position is reached where the torque generated by the torque motor and force exerted by the fluid flow through the system are equal and opposite. This provides a unique relationship between current input to the servo valve and the desired fluid flow through the servo valve.
In order for this system to operate properly a supply of high pressure fluid referenced to a low pressure fluid should be provided. The difference between the high pressure fluid and the low pressure fluid being used to control the position of the spool in the spool valve.
In operation the desired fluid flow in the high pressure side of the servo valve should not be allowed to leak into the low pressure side of the servo valve. If this happens large inaccuracies in the desired fluid flows from the servo valve will result. In the past any attempts to provide sealing between the high and lower pressure system has proved extremely difficult due to the necessary movement required in the feedback arrangement.
With conventional designs of servo valve it is very difficult to use the servo valve in association with a low pressure fluid flow system and a high pressure fluid flow system simultaneously, and in any event will add considerable weight and volume to the servo valve used in the system.
As will be appreciated by those in the aerospace industry weight and space are at a premium on an aircraft.